So yeah, my GameBoy has black smudges and horizontal lines. I've seen fixes for vertical lines, but I haven't seen any for horizontal lines. Is it possible to get a replacement LCD? Here is a picture.
Possibly, but you might have better luck on a Game Boy forum rather than NESdev...
Don't mean to be rude, but could you please give me a way to fix it?
Yeah, but I can't find a place where I can buy a replacement LCD. They have them for Gameboy Color and Advance, but none for the original.
You can not get a replacement LCD. At best you can salvage one from another Game Boy, or painstakingly solder in a Game Boy Pocket LCD, for which instructions are not provided.
The splotch is a "bubble" in the liquid crystal layer. That can not be repaired. Vertical lines may be repaired by hand. Nobody has made consistent results for fixing horizontal lines, though.